Pros
Colleagues in general are friendly and experts in their field. This provides ample opportunity to master your domain and learn valuable consulting skill sets if you are willing to apply yourself.
Cons
As stated by many other reviewers, ICF materially underpays its staff compared to competitors and the market. This is driven in large part because of the large volume of US federal work that provides the bulk of the company's revenue. Senior management seem to think that all consultants, even those in the high margin commercial sectors, should be paid the same as those doing low margin agency work for the government. Many of the best employees are therefore soon tempted away by competitors. Perhaps for the reason outlined above, or because the most hard working and ambitious people overlook ICF when searching for a job, there is very much a "that will do" culture. People do not strive to improve processes or enhance product offerings that are now approaching obsolescence in the current market.